CR, hyperactivity and stress

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Hi All,

It seems that stress may be involved in observations that CR can result in

increased

physical activity. This may represent a model for anorexia nervosa in which

some

patients go to extremes with exercise levels.

Different strains of rats were useful to show the result. Our cortisol hormone

levels in particular CRers may render individual CRers to increased

hyperactivity.

See the paper for which the pdf in not available below.

Duclos M, Bouchet M, Vettier A, D.

Genetic Differences in Hypothalamic-Pituitary-Adrenal Axis Activity and Food

Restriction-induced Hyperactivity in Three Inbred Strains of Rats.

J Neuroendocrinol. 2005 Nov;17(11):740-52.

PMID: 16219003

We used three inbred rat strains known for significant differences in the

activity

and reactivity of their hypothalamic-pituitary-adrenal (HPA) axis to stress

[Fischer

344 (F344), Brown Norway (BN) and (Lew) rats] to search for a strain

difference in the paradoxical increase in running activity induced by food

restriction and to explore the role of the HPA axis in this behaviour. Rats were

randomly assigned to either an ad lib sedentary group (AL), a control wheel

activity

group (ACT), a food restriction-induced hyperactivity group (FR-ACT) group (1.5

h/day ad lib food, 22.5 h/day ad lib wheel access) or a pair-fed group (FR). The

BN

and Lew rats reached the 25% body weight-loss criterion of FR-ACT (strain

effect:

F(2,132) = 45.58, P < 10-6) faster than the F344 strain due to higher food

restriction-induced running activity (strain effect: F(2,65) = 17.43, P =

0.00001).

FR and FR-ACT decreased thymus weight (marker of integrated HPA axis activation)

in

all strains. In Lew and BN strains, FR-ACT induced a further decrement on thymus

weight compared to their FR group. Prefeeding corticosterone levels (15.00 h)

increased during the study in BN and Lew FR-ACT rats, but not in F344. Total

wheel

turns were correlated to both final adipose weight (r = -0.49, P = 0.002) and

thymus

weight decrement (r = 0.59, P = 0.0001), emphasizing the relationship between

fat

mass and HPA axis activation in excessive running activity. Increased running in

conditions of food restriction and HPA axis activation may be linked at the

level of

the central nervous system. However, the involvement of corticotrophin-releasing

hormone, agouti-related peptide or cocaine- and amphetamine-regulated transcript

in

behavioural disturbances of FR-ACT rats was excluded (in situ hybridization). We

propose that corticosterone may be the link between initial low levels of fat

mass

and/or rate of fat mass loss (peripheral energy stores) and increased wheel

activity, favouring fueling through lipolysis and proteolysis and reinforcing

the

self starvation via reward mechanisms, thus establishing a deleterious vicious

cycle.

Al Pater, PhD; email: old542000@...

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